1. Field of the Invention
The invention is related to a shaft mounted rotor brake with the features of the preamble of claim 1.
2. Description of Related Art
Rotor brakes are used in helicopters and in some types of helicopters they even are a safety-relevant system.
The document DE 693 11 484 T2 discloses a transmission with integrated brake particularly usable for vehicles. The transmission includes, in an oil bath inside a containment and support casing, an epicyclic reduction unit which is kinematically connectable to a drive unit by means of at least two gears, of which the driven one is axially fixed, is coaxial to a sun gear of the reduction unit and is associated therewith by means of a splined coupling. A disk brake is arranged between the epicyclic reduction unit and the driven gear and has at least one first disk rigidly coupled to an internally toothed ring gear which is rigidly coupled to the containment casing and at least one second disk which is rigidly coupled so as to rotate together with the driven gear. The disk brake is associated with axially movable packing pushers.
The document EP 0894 712 A2 discloses a helicopter rotor brake having a disk connected angularly to a helicopter rotor. A brake caliper has friction members cooperating with the disk; and an actuating device for moving the brake caliper, parallel to the plane of the disk, between a work position engaging the disk. The brake caliper may be operated to brake the rotor, and a release position releasing the disk and wherein any possibility of the friction members interacting with the disk is prevented.
The document DE 103 43 055 A1 discloses a rotor shaft mounted rotor brake with a braking force absorption element non-rotatable connected to said rotor shaft; a stationary brake actuator for hydraulically or mechanically actuating a braking force transmission element that is functionally coupled to the braking force absorption element so as to exert a braking effect; and at least one rotor speed-controlled, centrifugal force-actuated rotor brake deactivation device.
Rotor brakes for helicopters may only be deployed on the ground and only once the (main) rotor has reached a certain speed, which is usually 40% to 50% of the rated rotor speed. Such a limitation is meaningful since, due to aerodynamic forces, the rotor speed drops relatively quickly to about 40% to 50% of the rated rotor speed, but after that, it decreases only relatively slowly. Dimensioning rotor brakes that are already effective at 70% to 100% of the rated rotor speed would entail very strong brakes, a substantial weight of the rotor brake as well as increased manufacturing costs. Therefore, especially in the civilian sector, such a design is neither desired nor, as a rule, necessary.
With conventional rotor brake systems, actuating the rotor brake above a value of 40% to 50% of the rated rotor speed can lead to deformation of components of the rotor brake, particularly of the brake disc, due to excessive thermal loads, in this speed range, excessive braking energy is applied to the brake system. In the extreme case, the structure of safety-relevant brake components such as, for example, the brake disk or the brake drum, can be changed and fail. As an example, mention should be made of the fact that an actuation of the rotor brake at 70% rather than at 50% of the rated rotor speed means that approximately twice as much braking energy has to be absorbed by the rotor brake system.
An operating error can occur with conventional rotor brakes. For example, it is possible for the pilot to accidentally actuate the rotor brake during flight, leading to overheating of the brake system components. Or the rotor brake can be actuated on the ground above the permissible speed of approximately 40% to 50% of the rated rotor speed has been reached which, as already mentioned, might lead to an overheating of the brake system components. With hydraulically activated brakes, an erroneous actuation of the braking function can also occur due to a temperature-related increase in the pressure of the hydraulic system or a malfunction of the hydraulic system.